A similar sort of thing happened with my parents and older sister.
I was already moved out, and was about 23 at the time. My older sister was 26/27. She has Autism, but is high-functioning, and had a long-term job and a boyfriend. He was also on the spectrum, but undiagnosed, and generally higher functioning than her, not to mention almost a decade older.
According to my parents, she was treating the house like a hotel. Out working all day (fair enough) and then sitting in her room all evening, unwilling/unable to spend any time with our parents.
Our parents (who were both retired), decided they wanted to move 2 hours way to the countryside, and sister wasn't invited to come with them. They basically said, if she wanted to live in her own place like a hotel, she was more than welcome to, but not with them.
In the end she moved in with her boyfriend, who had his own house, and some 15 years later they are still living together and seemingly very happy. Although it seems more like a friendship than a relationship.
You are being very nice to consider your DS in this OP. But if he's holding down a job, plus a side hustle, drives and is basically functioning, it probably is time he grew up and moved out.